Open-source Zendesk alternatives

2 open-source alternatives to Zendesk, curated: Freescout, Zammad. Each is open-source; compare license and links below.

Tool	What it is	License	Open source
Freescout	OSS alt to Zendesk; ~4465 stars; via openalternative.co	AGPL-3.0	yes
Zammad	OSS alt to Zendesk; ~5834 stars; via openalternative.co	AGPL-3.0	yes

Positioning is each tool's own description; open-source status is evidence-based. See each linked entry for details.